Gonococci (Gc) rely on their surface constituents for those interactions with a human host that promote gonorrheal infection. Pili are thought to anchor Gc to human mucosal sites. But in vivo Gc rapidly and regularly change from synthesizing one pilin subunit to making another. This pilus subunit variation relies on recombinational interactions between the Gc genome's single complete pilin gene and one or another of its partial pilin genes. These "gene conversion" events lead to pilin structural diversity when either different partial pilin genes or different segments of an individual partial gene undergo nonreciprocal recombinational insertion into the complete pilin gene. Marked structural diversity occurs in pilin subunits of Gc causing gonorrheal infections in male volunteers; such amino acid sequence and antigenic changes occur within the carboxy-terminal one half of the pilin molecule and includes regions previously thought to be invariant. Outer membrane protein II (P.II) of Gc has a less clearly defined role in pathogenesis of gonorrhea, but one or more of these surface-exposed polypeptides is regularly expressed by Gc recovered from male urethral sites; these proteins likely aid colonization by virtue of the inter-Gc aggregation they effect. Control of each P.II is exerted by recombination-independent changes in the sequence of its respective gene. In Gc recovered from experimentally infected males, one or two P.II species were regularly expressed, and the Gc from each male preferentially expressed some, but not other, P.II moieties.